Hydraulic Fracture From the Interface of a Cased Well Bore

ABSTRACT: Hydraulic fracture initiation and propagation from a cased and perforated wellbore is strongly dependent on the influence of the steel casing, the cement between the casing and the rock, and the strength of the steel-cement and cement-rock interface bonds. 2D and 3D simulations are presented to illustrate the effects of the casing on both the stress in the rock and the subsequent fracture propagation. The well bore pressure necessary to induce tension in the rock can be reduced by adding perforations to the model. A casing reduces the stress transfer into the rock; however, poorly bonded interfaces between the casing and rock allow greater stress transfer into the rock. Fluid pressure in the interface changes the tangential stress distribution in the rock, creating a local increase in stress at the ends of the pressurized section and a reduction in stress over the pressurized area. A casing can alter the fracture propagation trajectory and delay fracture reorientation, depending on the strength of the interface bonds.